Factors associated with the risk of work related stairway falls were studied via analysis of videotape recordings of industrial worker usage of 31 flights of stairs. The selection of stair sites involved a focusing procedure to identify high risk locations that would represent the injury causing potential of industrial stairs and enable a higher than average yield of incidents. Videotapes were reviewed to identify all incidents (trips, falls, slips, missteps, and temporary instability). Characteristics of the 98 users with recorded incidents were compared to 98 comparisons. The incident group of workers tended to be those whose movement was impeded by others and who were older; nonincident workers tended to wear glasses and include very large or heavy individuals. Physical features of the stairways showing significant correlation with high incidence rate included higher effective riser height, less effective tread depth and, for descent, larger nosing projections. The safest stairs had an effective riser height not greater than 7 inches, an effective tread depth no less than 11 inches, and nosing projections less than 11/16 inches. Other major factors included tread materials, visual surroundings, and handrail use; lower incidence rates were observed with concrete or stone treads, unobscured straight ahead views, and nonusage of handrails.